To protect data confidentiality, cryptographic methods are widely used, however, traditional methods require a higher level of computational resources to achieve a higher level of security. For this reason, ECC (Elliptic Curves Cryptography) is considered as a promising solution. This paper shows a systematic review about ECC methods for IoT systems. Our research questions were related to find out the principal applications of ECC, criteria for implementing ECC and the appropriate elliptic curves for lightweight devices. The papers were collected from Scopus, Science Direct and SpringerLink and after doing the study, we conclude that IoT is the principal application of ECC, the processing time is the most common implementation criteria and the Koblitz elliptic curve over prime fields are accurate for IoT.